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At least 1,009 records · Page 56Linked to original sources
PubMed1990

The influence of proline residues on alpha-helical structure.

Proline lacks an amide proton when found within proteins. This precludes hydrogen bonding between it and hydrogen bond acceptors, and thus often restricts the residue to the first four positions of an alpha-helix. Helices with proline after position four have a pronounced kink [(1988) J. Mol. Biol. 203, 601-619]. In these cases, we find that the proline residue almost almost always occurs on the solvent exposed face of each helix. This positioning facilitates the compensatory hydrogen bonding between solvent and residues P-3 and P-4 (relative to proline, P), through the formation of the kink. Further, it aids in the packing of long helical structures around globular protein structures.

Citrate (si)-Synthase↗
PubMed1993

H(+)-coupled (Na(+)-independent) proline transport in human intestinal (Caco-2) epithelial cell monolayers.

Previously, absorption of L-proline across the apical membrane of the intestinal enterocyte has been attributed to transport via the Na(+)-dependent Imino system. However, net (absorptive) transport of proline across intact Caco-2 cell monolayers was enhanced by acidification of the apical environment, under both Na(+)-containing and Na(+)-free conditions. This Na(+)-independent pH-dependent proline flux was associated with H+ flow across the apical membrane as determined by continuous measurement of intracellular pH. H+/proline symport was associated with an inward Isc in voltage-clamped Caco-2 epithelial layers demonstrating the electrogenic nature of this transport process. In conclusion Caco-2 cells possess an apically-localised, Na(+)-independent, electrogenic H+/imino acid transporter which may play an important role in intestinal proline absorption.

Biological Transport↗
PubMed1991

Proline kinks in transmembrane alpha-helices.

Integral membrane proteins often contain proline residues in their presumably alpha-helical transmembrane segments. This is in marked contrast to globular proteins, where proline is rarely found inside alpha-helices. Proline residues cause kinks in helices, and, in addition to leaving the i-4 backbone carbonyl without its normal hydrogen bond donor, also sterically prevent the (i-3)-carbonyl-(i + l)-amide backbone hydrogen bond from forming. Here, some structural aspects of proline kinks in transmembrane helices are discussed on the basis of an analysis of Pro-kinked helices in the photosynthetic reaction center and bacteriorhodopsin, as well as results from an analysis of Pro-containing transmembrane segments identified in the NBRF Protein Sequence Databank.

Amino Acid Sequence↗
PubMed1985

The influence of prostaglandin E2 and oxytocin on the incorporation of [3H]proline and [3H]glucosamine in the human amnion.

Fetal membranes were obtained in connection with 1st-trimester abortion and vaginal delivery or elective caesarean section at term. Pieces of the isolated amnion membrane were incubated in vitro with [3H]proline or [3H]glucosamine in the presence of prostaglandin (PG) E2 or oxytocin. PGE2 reduced the labelling with [3H]proline in the 1st trimester and in membranes obtained at vaginal delivery, whereas an increase of incorporation was observed before start of labour. Oxytocin reduced [3H]proline labelling at any stage. In membranes from vaginally delivered women both oxytocin and PGE2 stimulated the incorporation of [3H]glucosamine, whereas oxytocin diminished radiolabelling in the other experimental groups. Regarding the radiolabelling with [3H]proline and [3H]glucosamine as reflecting the de novo formation of collagen and proteoglycans, respectively, it is suggested that both PGE2 and oxytocin, by their influence on connective tissue metabolism, may regulate the tensile properties of the fetal membranes.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1984

Effect of proline analogs on oxygen toxicity-induced pulmonary fibrosis in the rat.

Proline analogs inhibit collagen biosynthesis and prevent accumulation of collagen in tissues. The antifibrotic effects of three proline analogs, cis-hydroxyproline, L-azetidine-2-carboxylic acid, and L-3,4-dehydroproline, were compared in a rat oxygen toxicity model. The specificity of these agents for collagen was examined by measuring their effects on noncollagen protein and elastin accumulation in the lung. Increased lung collagen was produced by exposing rats to 95% O2 for 60 hr followed by a 2-week recovery period. Animals were treated with the proline analogs for the 2-week period. Oxygen exposure in untreated animals increased lung collagen 26% above air-breathing controls, and this increase was prevented by all three analogs. Increased noncollagen protein was also prevented by these agents, suggesting they were not entirely specific for collagen. Elastin accumulation, however, was not inhibited by cis-hydroxyproline. It was concluded that proline analogs were antifibrotic, but affected the metabolism of noncollagen protein.

Animals↗
PubMed1989

Effect of proline administration on rat behavior in aversive and nonaversive tasks.

Sustained levels of proline comparable to those of human type II hyperprolinemia were achieved in blood and brain of rats subcutaneous proline administration twice a day from the 6th till the 28th day of life. Control rats were treated with saline in the same volumes. Behavioral studies using aversive and nonaversive tasks were performed one week or one month after treatment. Proline treatment did not affect rats' performance in the inhibitory avoidance task, but reduced significantly habituation in the open field. Our results seem to indicate that early postnatal administration of proline to rats affects habituation to a novel environment. If this happens to be so the present tendency to consider hyperprolinemia as a benign condition should be revised.

Age Factors↗
PubMed1994

Structural basis for the binding of proline-rich peptides to SH3 domains.

A common RXL motif was found in proline-rich ligands that were selected from a biased combinatorial peptide library on the basis of their ability to bind specifically to the SH3 domains from phosphatidylinositol 3-kinase (PI3K) or c-Src. The solution structure of the PI3K SH3 domain complexed to one of these ligands, RKLPPRPSK (RLP1), was determined. Structure-based mutations were introduced into the PI3K SH3 domain and the RLP1 ligand, and the influence of these mutations on binding was evaluated. We conclude that SH3 domains recognize proline-rich motifs possessing the left-handed type II polyproline (PPII) helix conformation. Two proline residues directly contact the receptor. Other prolines in the ligands appear to function as a molecular scaffold, promoting the formation of the PPII helix. Three nonproline residues consisting of combinations of arginine and leucine interact extensively with the SH3 domain and appear to confer ligand specificity.

Amino Acid Sequence↗
PubMedDate not supplied

Networking with proline-directed protein kinases implicated in tau phosphorylation.

Proline-directed kinases such as the mitogen-activated protein (MAP) kinases, cyclin-dependent protein kinase 5 (CDK5) and glycogen synthase 3 (GSK3) have been implicated in the hyperphosphorylation of the tau protein associated with Alzheimer's disease. Such aberrant phosphorylation of tau appears to compromise on its ability to bind to and stabilize microtubules, and this may contribute to Alzheimer's disease pathology. In this review, the architecture of the intracellular signal transduction pathways that regulate proline-directed kinases is described. The MAP kinases serve as major intersection points in the flow of information from a plethora of extracellular stimuli and affect diverse cellular processes that are often important for cell proliferation. Although brain contains terminally differentiated neurons, many of the known components of MAP kinase-dependent lines of communication are highly expressed in the nervous system. Similar signalling pathways may also regulate CDK5 and GSK3. In mitotic cells, abnormal activation of the protein kinase network at multiple points can contribute to oncogenic transformation. It is proposed that Alzheimer's disease may also result from accumulated defects in the kinase network that governs the proline-directed kinases such that their inappropriate activation is sustained in the affected neurons. A detailed understanding of proline-directed kinase-dependent pathways may permit the identification of rational targets for the therapeutic intervention of Alzheimer's disease and other neurological disorders.

Amino Acid Sequence↗
PubMed1985

Ciliary ganglia and spinal cord explants release an ascorbate-like compound which stimulates proline hydroxylation and collagen formation in muscle cultures.

A low-molecular-weight factor from embryonic rat brain stimulates collagen production in rat muscle cultures. This effect is associated with increased hydroxylation of proline residues in collagenous proteins produced by the cells. Here, we show that increased hydroxylation (22-and 7.5-fold) was also observed with extracts of rat embryonic spinal cord and extracts of the rat pheochromocytoma cell line PC12. A 5-25-fold stimulation in proline hydroxylation was obtained when muscle cells were cocultured with chick ciliary ganglia or with embryonic rat spinal cord explants. Medium conditioned by rat spinal cord explants also increased prolyl hydroxylation. Incubation of the muscle-nerve cocultures with ascorbate oxidase markedly reduced the observed increase in proline hydroxylation. These results show that the cultured explants release a factor which promotes proline hydroxylation and collagen production by muscle. This factor seems to be ascorbic acid or an ascorbate-like compound.

Animals↗
PubMed1994

Glycine betaine and proline betaine in human blood and urine.

In healthy human subjects, glycine betaine concentrations in the blood plasma are normally between 20 and 60 mumol/l, adult males tending to have higher concentrations than females. Proline betaine concentrations are more variable, ranging from undetectable to about 50 mumol/l. Both betaines are present in urine. Whereas the urinary excretion of proline betaine reflects plasma concentrations, with high clearance rates, there is no correlation between plasma and urine glycine betaine concentrations. The apparent clearance rates are low (usually less than 5%). The proline betaine content of human kidney tissue is less than 0.1% of the glycine betaine content, and this is true also of rabbit tissue despite high concentrations of both betaines in rabbit circulation and urine. These data suggest that glycine betaine, but not proline betaine, is important in human and other mammalian biochemistry.

Adolescent↗
PubMed1986

The oxidation of proline by mitochondrial preparations.

The oxidation by mitochondria of various rat tissues of proline, pyrroline-5-carboxylate (P5C) and a number of aldehydes has been studied and ADP/O ratios determined for liver mitochondria. High oxidative activity for proline and P5C was found only in the liver and kidney. During the oxidation by liver and kidney mitochondria of proline and P5C; glutamate, ammonia, aspartate and some ornithine accumulated, thus suggesting that proline may normally be converted to ornithine by mitochondria. The oxidation of P5C (glutamic acid semialdehyde) by a mitochondrial dehydrogenase may be the same enzyme that oxidizes succinic acid semi-aldehyde but different from that oxidizing acetaldehyde.

Aldehyde Dehydrogenase↗
PubMed1985

Identification of a mutation that relieves gamma-glutamyl kinase from allosteric feedback inhibition by proline.

A 1.75-kb DNA fragment containing the entire Escherichia coli proB+ gene has been sequenced. The proB locus encodes the structural gene for gamma-glutamyl kinase (GK), the enzyme responsible for the first step in proline biosynthesis, and the primary regulatory point of the pathway. We have previously reported the nucleotide (nt) sequence of a mutant proB gene isolated from an E. coli strain resistant to the toxic analog of proline, 3,4-dehydro-DL-proline (DHP). This mutant gene encodes a GK which is refractory to allosteric feedback inhibition by proline (DHPR). Comparison of the proB+ and DHPR proB sequences revealed a single base difference, an A-T to C-G transversion localized at nt position 428 within the amino acid (aa) coding region of proB. This mutation predicts an aa change from glutamic acid in the wild-type (wt) enzyme to alanine in the DHPR enzyme.

Allosteric Regulation↗
PubMed1993

Reversed-phase high-performance liquid chromatographic analysis of hydroxyproline and proline from collagen by derivatization with dabsyl chloride.

A high-performance liquid chromatographic method for the analysis of hydroxyproline and proline has been developed. The method is based on the derivatization of the secondary amino group with dabsyl-chloride after blocking of the primary amino group with o-phthalaldehyde. Dabsyl-hydroxyproline and dabsyl-proline were separated from other amino acids by high-performance liquid chromatography in the gradient elution mode, and eluted at 10.27 and 16.02 min, respectively. The correlations between the peak areas of dabsyl-hydroxyproline and dabsyl-proline were linear in the range from 20-200 pmol, with equations y = 1.10x - 0.80 (r = 0.999) and y = 1.12x - 0.52 (r = 0.999), respectively. The method was applied to the analysis of rat tail collagen, and the contents of hydroxyproline and proline were 1.55 +/- 0.04 and 2.03 +/- 0.04 nmol/micrograms, respectively.

Animals↗
PubMed1991

Effect of chlorpromazine on proline absorption across rat jejunum.

The effect of chlorpromazine on proline absorption across jejunum in anaesthetized rats was investigated. Intravenous infusion of chlorpromazine reduced significantly (P less than 0.01) proline absorption across the jejunum. Intraluminal perfusion of chlorpromazine into the jejunal segment reversed net absorption of proline to net secretion. Net water absorption was increased significantly (P less than 0.01) when chlorpromazine was infused intravenously or perfused intraluminally. Unidirectional influx of proline across the mucosal surface was significantly inhibited (P less than 0.01) after preincubation with 1 mM chlorpromazine.

Animals↗
PubMed2006

Diastereoselective synthesis of glycosylated prolines as alpha-glucosidase inhibitors and organocatalyst in asymmetric aldol reaction.

1,3-Dipolar cycloaddition of azomethine ylides and glycosyl E-olefins in presence of LDA led to diastereoselective formation of C-glycosylated proline esters. The selected esters on regioselective hydrolysis with LiOH gave C-glycosyl prolines. Few of the proline esters exhibited very good alpha-glucosidase inhibitory activity. The organocatalytic activity of the proline derivatives in a prototype Aldol reaction has also been investigated.

Aldehydes↗
PubMed2006

Immunohistochemical evidence for the localization of neurons containing the putative transmitter L-proline in rat brain.

We examined whether there are the neurotransmitter candidate amino acid L-proline containing neurons localized in the rat brain. Antibodies against L-proline conjugated with rabbit serum albumin were raised in a rabbit and purified with affinity chromatography. Strong L-proline-like immunoreactivity was confined to several groups of neurons in the arcuate nucleus (n) and supraoptic n in the hypothalamus and area postrema. The brainstem had markedly stained fibers in the medial longitudinal fasciculus and localized neuronal cell body labeling in the red n, mesencephalic trigeminal n, lateral reticular n, raphe obscurus n, solitary n, compact ambiguus n, motor trigeminal n and n of trapezoid body. Our findings are consistent with the hypothesis that L-proline may function as a neurotransmitter or neuromodulator in the brain.

Animals↗
PubMed2005

Temperature-responsive stationary phase utilizing a polymer of proline derivative for hydrophobic interaction chromatography using an aqueous mobile phase.

A new method of chromatography is proposed, utilizing a thermo-responsive polymer carrying an amino acid ester residue for the stationary phase of high-performance liquid chromatography (HPLC). We have been investigating the new concept of chromatography, a temperature-responsive chromatography, using temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm)-modified surface for HPLC with a constant aqueous media as the mobile phase. In this study, we designed and synthesized thermo-responsive poly(acryloyl-L-proline methyl ester) and its copolymer with N-isopropylacrylamide (NIPAAm). Homopolymers of acryloyl-L-proline methyl ester and copolymer were prepared by the reaction of radical telomerization. These polymers underwent a reversible phase transition from water-soluble forms into aggregates by changing the temperature, similar to PNIPAAm. The surface properties and functions of stationary phases modified with poly(acryloyl-L-proline methyl ester) were controlled by the external temperature. In the chromatographic system, we separated steroids and amino acids with a variety of hydrophobicities using a sole aqueous mobile phase. In contrast to a PNIPAAm-modified surface, a poly(acryloyl-L-proline methyl ester)-modified surface showed a greater affinity for hydrophobic amino acids.

Chromatography, Liquid↗
PubMed2006

Improvement of proline chiral stationary phases by varying peptide length and linker.

Seven new stationary phases with different number of proline units and/or different linkage to silica gel were prepared and evaluated in order to improve the performance of proline chiral stationary phases. The average separation factor achieved with the 53 analytes increases with the number of proline units in the stationary phases. When the proline peptides are directly attached to the 3-methylaminopropyl silica gel without using the 6-methylaminohexanoic acid linker, the stationary phases perform better overall. For decaproline chiral stationary phase 8, the separation also depends on the mobile phase system used. For this stationary phase, the CH2Cl2/hexanes/2-propanol system significantly outperforms the 2-propanol/hexanes system. For the 53 analytes tested, the separation factors achieved with this stationary phase compare well with those for three commercial columns.

Chromatography↗